1. Field of the Invention
The present invention relates to a plasma processing system, more particularly relates to a plasma processing system having a structure preventing the occurrence of undesirable discharge at a rear surface of a ground-side electrode when causing discharge by high frequency power in a chemical vapor deposition (CVD) chamber provided with a parallel plate electrode structure.
2. Description of the Related Art
A plasma film-deposition system having a parallel plate electrode structure comprised of two electrodes deposits a film on a substrate by placing the substrate on one of the two electrodes and generating plasma between the two electrodes. Since the one electrode functions as a substrate holder and is connected to a chamber held at the ground potential, it is held electrically at the ground potential. This electrode is called the xe2x80x9cground electrodexe2x80x9d. The other electrode is supplied with a high frequency power from a high frequency power source and is called a xe2x80x9chigh frequency electrodexe2x80x9d. A main discharge is generated in the space between the electrodes due to the high frequency power supplied to the high frequency electrode to generate plasma.
As references disclosing the prior art relating to the plasma processing system according to the present invention, Japanese Unexamined Patent Publication (Kokai) No. 10-237653 and Japanese Unexamined Patent Publication (Kokai) No. 10-237657 may be mentioned.
Japanese Unexamined Patent Publication (Kokai) No. 10-237653 discloses an invention preventing abnormal discharge in a vacuum processing system. The invention provides a vacuum processing system such as a plasma CVD system, which has the structure for covering the portion of a susceptor in the substrate holding and elevating members exposed from the substrate holding member by an insulating member. The susceptor mounts the substrate to be processed. The structure prevents the abnormal discharge between a substrate elevator member of the susceptor and a vacuum processing chamber. The abnormal discharge occurs when a high frequency voltage is applied to the susceptor.
Japanese Unexamined Patent Publication (Kokai) No. 10-237657 discloses an invention relating to a plasma processing system free from contamination or corrosion of a discharge-preventing plate. In this invention, there is provided a susceptor mounting a substrate and supplied with a high frequency voltage. The susceptor is arranged in a state with a discharge-preventing plate electrically insulated from a susceptor body. The discharge-preventing plate is arranged to be close to the surroundings of the susceptor body. It has a mechanism for passing a gas in the clearance between the susceptor body and the discharge-preventing plate. The discharge-preventing plate arranged in proximity to the susceptor body prevents the discharge which easily occurred between the susceptor and chamber upon the application of voltage to the susceptor because of a rise in the discharge generating voltage along with the Paschen""s law. There was however the problem that reaction products or corrosive gases would enter between the susceptor body and discharge preventing plate and therefore cause contamination or corrosion of the discharge-preventing plate. The above prior art solves this problem.
In a conventional plasma film-deposition system having a parallel plate electrode structure for depositing a film on a substrate, often a high frequency power, for example, a power of a high frequency of the VHF band (for example, 60 MHz) has been applied to the high frequency electrode. This was because high quality film-deposition characteristics were sought in the film deposited on the substrate. If the frequency of the high frequency power becomes higher, the input impedance (impedance as seen from opening) of the high frequency circuit comprised in the space between the ground electrode and the chamber becomes higher. As a result, the potential difference between the ground electrode and the chamber becomes greater and an undesirable discharge occurs at the rear surface of the substrate holder, that is, the ground electrode. This discharge has an effect on the main discharge occurring between the two electrodes and causes problems in the reproducibility and film-deposition characteristics in the film deposition on the substrate.
Further, along with an enlargement in size of substrates in recent years, it has become necessary to increase the high frequency current supplied to maintain a constant current density on the substrate. If the high frequency current is increased, undesirable discharge occurs due to the same action as above and the same problems as above occur.
If considering the inventions disclosed in the above known references from the viewpoint of solving the problems in the conventional plasma film-deposition system having the parallel plate electrode structure, each invention deals with problems relating to undesirable discharge occurring at the high frequency electrode. Further, they does not relate to undesirable discharge relating to the path through which the high frequency power is propagated from the ground electrode to the chamber of the ground potential at the rear surface of the ground electrode. In particular, as explained above, it is difficult for the plasma processing systems disclosed in the above references to prevent undesirable discharge at the rear surface of the ground electrode. The undesirable discharge occurs in relation to the higher level of discharge frequencies. The higher discharge frequency follows the enlargement in the size of the substrates or demands for high quality film characteristics. That is, it is not possible to completely prevent undesirable discharge from occurring at the rear surface of the ground electrode by the configurations disclosed in the above references.
An object of the present invention is to provide a plasma processing system designed to reliably prevent undesirable discharge from occurring at the rear surface of a ground electrode when performing processing to deposite a film on a substrate mounted on the ground electrode using a high frequency power of a frequency in the VHF band.
The plasma processing system according to the present invention is configured as follows so as to achieve the above object.
The plasma processing system of the present invention is comprised of a chamber in which are provided a high frequency power source side electrode (called a xe2x80x9chigh frequency electrodexe2x80x9d) and a ground side electrode (called a xe2x80x9cground electrodexe2x80x9d). Normally, the high frequency electrode is provided at a ceiling of the chamber, while the ground electrode is provided at the bottom of the chamber. The high frequency electrode and the ground electrode are arranged in parallel. A column made by a conductive member supports the ground electrode. The support column is affixed to part of the chamber held at the ground potential. The chamber corresponds to the ground potential portion. Further, the support column is actually structured to move up and down by an elevator mechanism. The ground electrode also moves up and down simultaneously due to the up and down motion of the support column. The substrate to be processed is mounted on the ground electrode. The ground electrode therefore has the function of a substrate holder. The substrate is a large area substrate having a relatively large diameter. Corresponding to this, the high frequency electrode is supplied with a relatively large high frequency power in order to maintain the power density on the substrate at a predetermined constant value. When causing discharge between the high frequency electrode and the ground electrode, the ground electrode on which the substrate is mounted is made to rise by the elevator mechanism. The movement by the elevator mechanism narrows the space between the two electrodes. The high frequency power is supplied from the high frequency power source under conditions of the required reduced pressure, discharge gas, and feedstock gas. In this way, discharge is caused between the two electrodes by the high frequency power supplied from the high frequency power source and the thus produced plasma is used to treat or process the substrate mounted on the ground side electrode. The characteristic feature of the configuration is as follows. The surface of the connection part from the ground electrode to the ground potential portions (portions other than surface of the ground electrode, support column, etc.) is covered by a high frequency power propagating medium. The surface of the high frequency power-propagating medium is covered completely by a conductor except the portion for introducing the high frequency power.
If main discharge is caused by supplying high frequency power to the space between the high frequency electrode and the ground electrode, the high frequency power propagates from the region where the main discharge occurs at the front surface of the ground electrode toward the ground potential portions. In the past, this caused undesirable discharge at the rear surface side of the ground electrode. According to the above configuration of the present invention, however, the high frequency power heading toward the ground potential portions propagates through the high frequency power-propagating medium. As a result, it is possible to reliably prevent the occurrence of undesirable discharge at the rear surface side or periphery of the ground electrode.
In the above configuration, preferably the high frequency power propagating medium covers the entire surface of the connection portion including the rear surface of the ground electrode. According to this configuration, the rear surface of the ground electrode and the entire surface of the connection portion are covered by the high frequency power-propagating medium. This is suitable for a small-sized film-deposition chamber.
In the above configuration, preferably the high frequency power propagating medium covers the entire surface of the connection portion including the side surfaces and rear surface of the ground electrode. According to this configuration, the side surfaces and rear surface of the ground electrode and the entire surface of the connection portion are covered by the high frequency power propagating medium and the structure on the ground electrode side becomes large, but this is suited for a large-sized film-deposition chamber. Further, since the surfaces are completely covered, this structure is desirable for when completely preventing discharge.
In the above configurations, the high frequency power propagating medium is preferably one of an insulator, a low pressure gas, and a composite of an insulator and a low pressure gas. In the case of a low-pressure gas, a space having a predetermined narrow width is formed, and the low-pressure gas enters into and fills that space. Even such a low-pressure gas acts as a high frequency power-propagating medium. Further, alumina is preferable as the above insulator.